The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
Previously we reported*1 to SPE'99 on the basic principles for optimization of the vibration welding process and presented an analysis of the weld-melt temperature kinetics for linear vibration welding. For this investigation we used the advanced Thermovision 900® infrared measurement system*2 for comprehensive, real-time analysis and thermal imaging. Under optimized processing conditions for vibration (linear and orbital) and hot-plate welding technologies, the tensile strength of welded nylon 6 butt joints is equal to or 14% higher than the tensile strength of the base polymer (matrix). For optimized vibration welding conditions, the maximum temperatures of the weld-melt (in inter-phase) were significantly above (85 - 90 °C) the melt point of the welded nylon 6 and nylon 66 (Tm = 223 °C and 261 °C, respectively). For PP based plastics, J. Vetter and G. W. Ehrenstein observed*3 an increase in the maximum temperature in the weld-melt / in weld inter-phase of not more than 10 °C above the melting point ( Tmp ). In their report to SPE'99, the authors discussed the results of the physical modeling for semi-crystalline HDPE, showing the values of maximum temperatures in the weld inter-phase above 250 °C compared to melting point (Tmp = 126 °C). Ch. Bonten presented*4 to SPE'99 his analysis on the mechanisms active in weld interface of semi-crystalline thermoplastics (HDPE and cross-linked polyethylene PE-X). Mechanical performance of welded joints was affected by crystallization across the boundary layer and weld-melt temperature kinetics (above melting point Tmp). For a better understanding of the role and influence of the temperature of the melt (in injection molding) and weld-melt (in welding) on mechanical performance of semi-crystalline molded (welded) thermoplastics, we performed a comparative study for nylon 6 and nylon 66 (non-filled and fiber-glass reinforced) plastics. Mechanical performance of injection molded and welded nylon was evaluated using static (tens
An integrated thermoforming simulation of a HDPE bass boat hull was performed. The part is fabricated by Pelican International. The sheet heating, forming and cooling stages were sequentially analysed in order to predict the sheet sag and temperature as well as the final part wall thickness distribution. Sheet heating includes radiation from the oven banks combined with air convection. The viscoelastic deformation of the polymer under gravity load was modelled in order to predict sheet sag in the oven. The effect of the sheet sag, for a long part (3 m), on the sheet deformation during the forming stage could then be predicted. The part thickness was measured with a magnetic sensor. These experimental values were then compared with the prediction. Good agreement between predicted and measured wall thickness distribution was found.
The dimensional recovery of biaxially oriented polystyrene and high impact polystyrene films was found to follow dual second order kinetic processes that took place in parallel. The early stage of the recovery involved major dimensional changes with a high rate constant and is likely related to the recovery of main chain orientation. The later stage process gave smaller dimensional changes with a low rate constant and is not directly related to the main chain orientation. This study indicated that the orientation in amorphous polymer films could be examined by understanding the kinetics of thermal recovery.
Large scale computational fluid dynamics (CFD) models, typically consisting of 100 thousands of cells, are used in the design process of plastic components. Readily available hardware and software have made it possible to simulate a system as a whole and determine the contribution and effect of each component onto the overall performance. The CFD tools are used primarily to guide making modifications to achieve better performance and to execute smarter validation test, thus eliminating unnecessary preliminary models. This paper presents a CFD guided case study on performance optimization, conducted on a centrifugal fan used in the cooling of a tractor engine.
This paper presents the latest development of a Web-based Knowledge Management System (KMS) for injection molding. This system is aimed at helping any knowledge-intensive organization in the molding industry to create, capture, manage, and share engineering data and know-how related to plastics part design and manufacturing (Molding Intelligence"). The KMS is implemented within the framework of the Internet and Web technologies to facilitate ease of use global and instant information access and dissemination and collaboration among geographically dispersed team members."
This paper discusses the role of injection and blow molding set-up in reducing the bottles' vulnerability to stress cracking; an aspect often ignored in traditional training on stress crack prevention. Case studies, involving process optimization for stress crack resistance, illustrate typical key process variables affecting stress cracking including interactions with injection molding variables. Examples show how to strike a balance between the demands of stress cracking performance and performance of other key areas. It comments on the relationship between stress crack resistance and properties such as material distribution and base clearance (the gap between the injection gate and the bottom of the bottle).
Sophistication of experimental designs for weathering research testing continues to evolve. The majority of current weathering experiments utilize simple designs which change few variables at a time. These types of weathering experiments require more trials and result in more cost and less information than approaches using Fractional Factorials." Conducting "Fractional Factorial" experiments before using traditional approaches focuses weathering research on the significant and important variables effecting material performance. This paper presents a methodology for applying "Screening Fractional Factorial" approaches to material performance research. This paper includes a case study and examples of weathering data."
In most analyses of the film casting process, edge effects such as necking in and edge beading are usually neglected. In this work, we investigated the significance of these effects and their dependence on the rheological properties of the melts, the draw ratio, and the extrusion rate. Two linear low-density polyethylene melts and a low-density polyethylene melt were considered. The rheological behaviors of these melts were characterized under shear and elongational flows. Streamlines from the die exit to the chill roll, velocity profiles, film tension, neck-in profiles, thickness profile of the solidified film, and edge bead thickness profile were examined.
Finite element simulation of thermoforming can provide highly accurate predictions of final part thickness. The majority of these simulations have been for isothermal situations. Similar calculations can also be performed for non-isothermal processing conditions, provided suitable temperature dependent material properties are available for the polymer of interest. For these simulations, it is assumed that the initial sheet temperature is known and does not change significantly during forming. In this paper sample results are presented for the so-called inverse thermoforming problem, where an initial temperature distribution is sought that will result in a specific final thickness distribution. Thus, a finite element simulation is combined with an iterative algorithm to obtain inverse solutions for a simple axisymmetric thermoformed part. In this example, the required initial temperature distributions that result in a uniform final thickness, are determined for a deeply drawn part. It is shown that the calculated results are quite sensitive to perturbations in the specified initial temperature profile and thus the practical application of optimal temperature distributions may require high precision thermal sensors and controls.
The objective of this research was to study the adhesion between a core (hard) material and skin (soft) material mainly used for the interior applications in automotive industry, using the two-shot injection molding process. Two different groups of materials were tested for the adhesive bond strength. In the first group, filled polypropylene (PP) and two thermoplastic polyolefins (TPO) were tested with two thermoplastic elastomers (TPE). In the second group, polycarbonate (PC), acrylonitrile butadiene styrene (ABS), and PC+ABS alloy were tested with thermoplastic polyurethane (TPU). Since many current applications involve the use of an elastomeric material as a skin material for a hard material, this research will provide some guideline for materials to be used, part design, process parameters, adhesive joint design, and post conditioning.
Typical consumer products cannot be produced as a single part. Most items require the manufacturing of multiple parts followed by an assembly procedure. Assembly methods vary depending on the nature of the parts and their end uses. Typical assembly methods utilize bosses with nuts and bolts, snap fits, ultrasonic or spin welding and press fits. This report addresses tests undertaken on a variety of plastics, to determine the viability of the patented kinetic weld process invented at Bell Labs, the research and development arm of Lucent Technologies. In order to develop design guidelines for kinetic welding it is necessary to test a wide range of materials with different pin and boss combinations. The first series of tests were performed with welds of three different materials at three different assembly pressures and two geometric configurations. It was found that materials with relatively higher impact strengths tend to perform better than less resilient ones. It was also found that numerical design guidelines were important in optimizing the dimensions of the pin, boss and weld so as to have equalized stress throughout the part.
An advanced PC/ABS blend has been developed offering reduced cycle times for injection molding applications, and thus creating economic value for the molder. This material has improved flow as compared to traditional PC/ABS blends, yet it is designed for high toughness. The results of molding trials demonstrate injection pressure and melt temperature can be reduced, ultimately resulting in reduced cycle time and improved manufacturing cost. Physical properties and desired part performance criteria, such as heat resistance and low temperature ductility, are maintained.
The application of hot melt adhesives is based on heating the adhesive from solid state to liquid state for wetting, and cooling back to its solid state to develop cohesive and adhesive strength. Conventional hot melt adhesive application methods use a separate heat source to melt the adhesive and apply it onto one of the substrates. Frequently, the adhesive cools while the second substrate is brought into contact with it resulting in inadequate wetting. With ultrasonic vibration, viscoelastic internal heating of the adhesive is used to melt it and to aid in wetting of the pre-placed hot melt adhesive film on the surfaces of both substrates. In this work, a conventional 40 kHz ultrasonic welder was used to heat a coated hot melt adhesive film in a laminate. The effects of the processing parameters of heating time, vibration amplitude, heating pressure, and hold pressure on bond performance were studied. It was found that the holding pressure plays an important role in sealing and bonding performance. Through the use of ultrasonic vibration it was possible to produce high quality seals in very short cycle times of less than 7 seconds.
Optimization of welding for thermoplastic parts strongly depends on the material properties, part design, as well as the welding operating technology conditions. Laser transmission welding requires preferential deposition of energy and subsequent melting of the material in the interfacial zone. This is optimized when the laser beam is transmitted through the transparent part and absorbed by the adjoining part to be welded. Energy deposition can be controlled to some extent by adjusting laser parameters (power, choice of beam focussing optics, sweep rate etc.) The thermoplastic material properties may have the greater influence and need to be characterized for optimum material selection. Commercial nylon type materials cover a large array of compositions, which may affect the welding process. To guide selection of nylon based plastics for a range of applications we have measured the influence of specific factors such as fiber-glass, mineral filler, impact modifier content, additives, and color versions on the Near InfraRed (NIR) transmission properties. In a following paper (Part II)a1 we have related these findings to the mechanical performance of shear and butt joints produced under various laser welding technology conditions (laser beam power, welding speed, laser beam/spot diameter, clamp pressure, plastic color, etc.). Comprehensive results of this evaluation will assist designers and technologists in thermoplastics selection for laser welding applications. The purpose of this report is to increase the understanding of the plastics engineering community regarding the usefulness and possible applicability of laser transmission welding (LTW) technology for nylon made components.
Hot plate welding is one of the most popular plastics joining methods and it is employed in most industries. Traditionally, the hot plate is coated with a non-stick" surface usually polytetrafluoroethylene (PTFE) which is usable to temperatures not exceeding 260°C. To avoid sticking to the hot plate and to accommodate higher hot plate temperatures non-contact hot plate is used. This paper is concerned with determining the optimum process parameters for non-contact hot plate welding of high-density polyethylene. For a given welding pressure the melt layer thickness weld displacement and their ratios were used as control or reduced parameters. During heating the melt layer thickness of the high-density polyethylene samples was measured. An empirical relationship between melt layer thickness and hot plate temperature and heating time was developed and used to predict the melt layer thickness in future experiments. The effects of the reduced welding parameters on joint quality are presented and compared with contact hot plate welding. For both processes the maximum attainable joint strength is 100% of the bulk material strength with the optimum melt layer thickness of 3.5 mm (1.75 mm for each part). The energy at break was more dependent on the ratio of weld displacement to melt layer thickness. For non-contact hot plate the optimum weld displacement melt layer thickness ratio was 0.75 compared to a ratio of 0.4 for contact hot plate welding.
During the production of plastic parts the presence of voids, inclusions, fiber reinforcement and fillers can play a critical role in the structural integrity of the product. Although in recent years tremendous improvements have been made in the field of analysis and design software to predict such factors, their physical detection is more difficult to accomplish. Certainly, when considering quality assurance and quality control, the ability to accurately and efficiently determine internal structure in a non-destructive manner is beneficial. This paper presents a novel method of using Computed Tomography (CT) to detect and visualize internal structure in polymer articles.
Biodegradable polymers are used in medical applications, among many reasons, because of their history of biocompatibility. In this report an attempt has been made to establish the structure created by reactive processing of poly (caprolactone) and Easter 14766 with dicumyl peroxide (DCP). Results showed that PCL quantitatively formed tetra-functional branches while the Easter 14766 formed a combination of tri and tetra-functional branch points. The Easter 14766 was also shown to be more reactive than the PCL, with half as much DCP being required to achieve equivalent amounts of branching. Both Easter 14766 and PCL displayed typical branching behavior with increase in melt elasticity and zero shear viscosity. Easter 14766 showed a little improvement in mechanical properties. However, studies showed PCL to be insensitive to branching.
Risk analysis techniques have become increasingly popular in the industrial sector, especially with the increasing number of mandated quality programs worldwide. Methods such as Failure Modes and Effects Analysis (FMEA), Fault Tree Analysis (FTA) and others are gaining wide recognition for their utility in product design. This paper discusses the practical use of risk analysis in plastic product systems as an up-front tool for design and product evaluation. Simplified techniques are presented which minimize the cumbersome nature of the risk analysis process and allow for more effective and efficient design and testing programs.
In recent years, the advance of high speed processors in personal computers has placed the capability of sophisticated analytical methods on nearly every desktop. In the plastics industry, codes are readily available to model, among other things, stresses, thermal characteristics and flow. Without proper input, however, such analyses are subjected to the Garbage In, Garbage Out (GIGO) syndrome and can produce misleading results. This paper discusses an approach to analytical modeling that includes experimentation for model input and constitutive model development, as well as the use of experimentation for verification of numerical modeling results.
The incorporation of glass fibers in a thermoplastic matrix improves its tensile properties but decreases the impact strength. The addition of a third component such as an elastomer generates a new material with improved impact resistance but poor mechanical properties. In this work, a rubber phase was added to a glass short fiber reinforced polypropylenes to obtain a material with balanced tensile and impact properties. Two different types of rubber was used and analyzed. Some composites with different concentration rubber/FV/PP was prepared and molded by injection. Its mechanical an impact behavior was studied and the processing window was analyzed.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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